Continuous packet connectivity (CPC) was introduced in Release 7 of the Third Generation Partnership Project (3GPP) standards. CPC reduces uplink interference created by dedicated physical control channels of packet data users when those channels have no user data to transmit. This, in turn, increases a supported number of simultaneously connected high-speed uplink packet access (HSUPA) users. CPC permits discontinuous uplink transmission and discontinuous downlink reception, where the user equipment can turn off its receiver after a certain period of high-speed downlink packet access (HSDPA) inactivity. CPC may be especially beneficial to voice over Internet protocol (VoIP) data packets provided on the uplink because the user equipment can turn off between VoIP data packets.
CPC attempts to reduce overhead in the uplink, increase the number of HSUPA/HSDPA users that can be kept in a cell dedicated channel (CELL_DCH) state, and reduce latency for restart after temporary inactivity. The overhead in the uplink results mainly from continuous transmission (e.g., by the user equipment) of a dedicated physical control channel (DPCCH) signal when data is not being transmitted. The DPCCH consists of both pilot bits and power control bits. The pilot bits are used for channel estimation and decoding of actual data. The DPCCH power control bits are used for adjusting the downlink power control. Thus, the DPCCH serves the purpose of maintaining synchronization and keeping power control ready when needed for rapid resumption of data transmission.
CPC utilizes a number of methods that attempt to make systems (e.g., a wideband code division multiple access (WCDMA) system, a high-speed packet access (HSPA) system, etc.) provide higher capacity and quality. One such method is referred to as user equipment (UE) discontinuous transmission and reception (DTX/DRX) (or “uplink DPCCH gating”). With UE DTX/DRX, the user equipment periodically sends (or “gates”) the power control (e.g., DPCCH) signaling (called “UE DTX bursts” in the 3GPP specifications) or sends the power control signaling when data is sent on an enhanced dedicated channel (E-DCH) dedicated physical data channel (E-DPDCH) or a high speed DPCCH (HS-DPCCH). UE DTX/DRX may use a UE DTX/DRX offset parameter to tailor the power control (e.g., DPCCH) signaling. Another method utilized by CPC is referred to as Node B (or downlink (DL)) discontinuous reception (DRX). In Node B DRX, data transmission (e.g., an E-DPDCH data transmission) may be held or delayed until the start of the next power control signaling burst (e.g., a DPCCH burst).
Both methods (e.g., UE DTX/DRX and Node B DRX) attempt to align the timing of data transmission (e.g., E-DPDCH transmission) with the timing of power control (e.g., DPCCH) signaling (the so called UE DTX burst). For example, both methods may attempt to align time slots (e.g., transmission time intervals (TTIs)) associated with the data transmission and the power control signaling. In UE DTX/DRX, a DPCCH preamble (e.g., of two time slots) and DPCCH postamble (e.g., of one time slot) must be sent before and after all data transmissions. In Node B DRX, the start of a data transmission coincides with the start of a DPCCH burst so that there is no DPCCH preamble, other than what is prescribed in the standard, before the data transmission and a longer DPCCH postamble after the data transmission.
Considerable gains can be achieved if the data transmissions (e.g., VoIP transmissions) are associated with DPCCH preambles exceeding the standard two time slot preamble. The optimal DPCCH preamble length may depend on channel conditions, the user equipment speed, and radio-specific configurations (e.g., open-loop power control (OLPC), retransmission/block error rate (BLER) targets, power offsets, etc.). However, according to the standard, it is not possible to obtain a preamble longer than the two time slot preamble. The two time slot preamble may be too short for certain data transmissions (e.g., for VoIP transmissions) in many cases. In such cases, the power control signal is unable to keep up with the quickly-changing radio conditions. For example, with a two millisecond (ms) TTI, there is a risk that a carrier to interference ratio (CIR) target is not met using the two time slot preamble. This means that there is a risk that a data packet may need to be retransmitted or may be lost. There is also a risk that the CIR target is raised, which results in reduced capacity.